diff --git a/dtls_debug.h b/dtls_debug.h
index 37a4731d..a02cab4e 100644
--- a/dtls_debug.h
+++ b/dtls_debug.h
@@ -129,8 +129,8 @@ void dtls_dsrv_log_addr(log_t level, const char *name, const session_t *addr);
 #define dtls_notice(...) LOG_INF(__VA_ARGS__)
 #define dtls_info(...) LOG_INF(__VA_ARGS__)
 #define dtls_debug(...) LOG_DBG(__VA_ARGS__)
-#define dtls_debug_hexdump(name, buf, length) { LOG_DBG("%s (%zu bytes):", name, length); LOG_HEXDUMP_DBG(buf, length, name); }
-#define dtls_debug_dump(name, buf, length) { LOG_DBG("%s (%zu bytes):", name, length); LOG_HEXDUMP_DBG(buf, length, name); }
+#define dtls_debug_hexdump(name, buf, length) { LOG_DBG("%s (%zu bytes):", name, (size_t)(length)); LOG_HEXDUMP_DBG(buf, length, name); }
+#define dtls_debug_dump(name, buf, length) { LOG_DBG("%s (%zu bytes):", name, (size_t)(length)); LOG_HEXDUMP_DBG(buf, length, name); }
 #elif defined(RIOT_VERSION)
 #define dtls_emerg(...) LOG_ERROR(__VA_ARGS__)
 #define dtls_alert(...) LOG_ERROR(__VA_ARGS__)
@@ -139,8 +139,8 @@ void dtls_dsrv_log_addr(log_t level, const char *name, const session_t *addr);
 #define dtls_notice(...) LOG_INFO(__VA_ARGS__)
 #define dtls_info(...) LOG_INFO(__VA_ARGS__)
 #define dtls_debug(...) LOG_DEBUG(__VA_ARGS__)
-#define dtls_debug_hexdump(name, buf, length) { if (LOG_DEBUG <= LOG_LEVEL) { LOG_DEBUG("-= %s (%zu bytes) =-\n", name, length); od_hex_dump(buf, length, 0); }}
-#define dtls_debug_dump(name, buf, length) { if (LOG_DEBUG <= LOG_LEVEL) { LOG_DEBUG("%s (%zu bytes):", name, length); od_hex_dump(buf, length, 0); }}
+#define dtls_debug_hexdump(name, buf, length) { if (LOG_DEBUG <= LOG_LEVEL) { LOG_DEBUG("-= %s (%zu bytes) =-\n", name, (size_t)(length)); od_hex_dump(buf, length, 0); }}
+#define dtls_debug_dump(name, buf, length) { if (LOG_DEBUG <= LOG_LEVEL) { LOG_DEBUG("%s (%zu bytes):", name, (size_t)(length)); od_hex_dump(buf, length, 0); }}
 #else /* neither RIOT nor Zephyr */
 #define dtls_emerg(...) dsrv_log(DTLS_LOG_EMERG, __VA_ARGS__)
 #define dtls_alert(...) dsrv_log(DTLS_LOG_ALERT, __VA_ARGS__)